The objective of this study is to develop and validate biomarkers that reflect mechanisms of biological aging. At least five pharmacologic compounds approved for human use extend health span and life span in rodent models. Parallel approaches in humans would require studies lasting 40+ years and are infeasible. Rather, the field needs reliable human biomarkers that indicate beneficial (or adverse) effects of an intervention on aging-related pathways over shorter time periods. Epigenomics and resultant transcriptomic changes may unite mechanisms of biological aging implicated in animal studies and unravel novel pathways. In a genome- wide analysis of monocyte samples in 1,200 persons (aged 55-94 years) from the Multi-Ethnic Study of Atherosclerosis (MESA), we identified 1,794 age-associated methylation sites and 2,704 age-associated transcripts, which over-represented several networks, including mitochondrial bioenergetics and autophagy. We further demonstrated associations of these gene networks with aging-related diseases independent of age. In addition to omic profiles, functional phenotyping may provide further advantages as biomarkers of the aging process. For example, our studies in older adults indicate the bioenergetic capacity of peripheral blood mononuclear cells is positively associated with physical function measures even when controlling for age. We predict that these epigenetic, transcriptomic, and functional markers will be associated with the development of aging-related comorbidities and are responsive to caloric restriction. We propose to utilize existing longitudinal assessments of monocyte epigenetic/transcriptomic profiles and age-related health outcomes from 1,800 middle-aged and older adults (55-94 years) in the MESA study. Leveraging an ongoing randomized clinical trial (VEGGIE) of caloric restriction in 200 adults (40-70 years), we also propose to add skeletal muscle biopsy (N=80). The specific aims are: 1) to determine whether aging-related monocyte transcriptomic/epigenomic pathways individually or in combination predict changes in aging-related diseases over an 8-year follow up (N=1,800); and 2) To determine whether caloric restriction shifts aging-related monocyte transcriptomic/epigenomic pathways (N=200) and bioenergetic measures in circulating cells and skeletal muscle (N=80) towards a younger pattern and whether these changes individually or in combination correlate with changes in aging-related metabolic, physical and cognitive health outcomes. The proposed study will generate a panel of biomarkers reflecting a comprehensive battery of aging pathways by integrating transcriptomic and epigenomic profiles with bioenergetics in circulation and skeletal muscle, from an existing longitudinal cohort study and an ongoing clinical trial of caloric restriction, to efficiently and cost-effectively validate potential biomarkers through multiple convergent strategies.